Method and apparatus for handling feedback resource for groupcast in sidelink in a wireless communication system

ABSTRACT

A method and apparatus are disclosed from the perspective of a first device to determine sidelink feedback resource associated with sidelink communication. In one embodiment, the method includes the first device receiving an identifier from an upper layer of the first device. The method also includes the first device receiving a sidelink transmission from a second device. The method further includes the first device determining a sidelink feedback resource associated with the sidelink transmission at least based on the identifier and a source ID (Identity) associated with the sidelink transmission. In addition, the method includes the first device using the sidelink feedback resource to transmit a feedback in response to the sidelink transmission to the second device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present Application is a continuation of U.S. patent applicationSer. No. 16/892,850, filed Jun. 4, 2020, which claims priority to andthe benefit of U.S. Provisional Patent Application Ser. No. 62/859,308,filed Jun. 10, 2019, with the entire disclosure of each referencedapplication fully incorporated herein by reference.

FIELD

This disclosure generally relates to wireless communication networks,and more particularly, to a method and apparatus for handling feedbackresource for groupcast in sidelink in a wireless communication system.

BACKGROUND

With the rapid rise in demand for communication of large amounts of datato and from mobile communication devices, traditional mobile voicecommunication networks are evolving into networks that communicate withInternet Protocol (IP) data packets. Such IP data packet communicationcan provide users of mobile communication devices with voice over IP,multimedia, multicast and on-demand communication services.

An exemplary network structure is an Evolved Universal Terrestrial RadioAccess Network (E-UTRAN). The E-UTRAN system can provide high datathroughput in order to realize the above-noted voice over IP andmultimedia services. A new radio technology for the next generation(e.g., 5G) is currently being discussed by the 3GPP standardsorganization. Accordingly, changes to the current body of 3GPP standardare currently being submitted and considered to evolve and finalize the3GPP standard.

SUMMARY

A method and apparatus are disclosed from the perspective of a firstdevice to determine sidelink feedback resource associated with sidelinkcommunication. In one embodiment, the method includes the first devicereceiving an identifier from an upper layer of the first device. Themethod also includes the first device receiving a sidelink transmissionfrom a second device. The method further includes the first devicedetermining a sidelink feedback resource associated with the sidelinktransmission at least based on the identifier and a source ID (Identity)associated with the sidelink transmission. In addition, the methodincludes the first device using the sidelink feedback resource totransmit a feedback in response to the sidelink transmission to thesecond device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram of a wireless communication system according toone exemplary embodiment.

FIG. 2 is a block diagram of a transmitter system (also known as accessnetwork) and a receiver system (also known as user equipment or UE)according to one exemplary embodiment.

FIG. 3 is a functional block diagram of a communication system accordingto one exemplary embodiment.

FIG. 4 is a functional block diagram of the program code of FIG. 3according to one exemplary embodiment.

FIG. 5 is a reproduction of FIG. 4.2.1.1-1 of 3GPP TS 23.287 V1.0.0.

FIG. 6 is a reproduction of FIG. 6.3.2-1 of 3GPP TS 23.287 V1.0.0.

FIG. 7 is a reproduction of FIGS. 5.1-1 of 3GPP TR 38.885 V16.0.0.

FIG. 8 is a reproduction of FIGS. 5.1-2 of 3GPP TR 38.885 V16.0.0.

FIG. 9 is a diagram according to one exemplary embodiment.

FIG. 10 is a diagram according to one exemplary embodiment.

FIG. 11 is a diagram according to one exemplary embodiment.

FIG. 12 is a diagram according to one exemplary embodiment.

FIG. 13 is a diagram according to one exemplary embodiment.

FIGS. 14A and 14B are diagrams according to one exemplary embodiment.

FIG. 15 is a diagram according to one exemplary embodiment.

FIG. 16 is a diagram according to one exemplary embodiment.

FIG. 17 is a flow chart according to one exemplary embodiment.

FIG. 18 is a flow chart according to one exemplary embodiment.

FIG. 19 is a flow chart according to one exemplary embodiment.

FIG. 20 is a flow chart according to one exemplary embodiment.

FIG. 21 is a flow chart according to one exemplary embodiment.

FIG. 22 is a flow chart according to one exemplary embodiment.

DETAILED DESCRIPTION

The exemplary wireless communication systems and devices described belowemploy a wireless communication system, supporting a broadcast service.Wireless communication systems are widely deployed to provide varioustypes of communication such as voice, data, and so on. These systems maybe based on code division multiple access (CDMA), time division multipleaccess (TDMA), orthogonal frequency division multiple access (OFDMA),3GPP LTE (Long Term Evolution) wireless access, 3GPP LTE-A orLTE-Advanced (Long Term Evolution Advanced), 3GPP2 UMB (Ultra MobileBroadband), WiMax, 3GPP NR (New Radio), or some other modulationtechniques.

In particular, the exemplary wireless communication systems devicesdescribed below may be designed to support one or more standards such asthe standard offered by a consortium named “3rd Generation PartnershipProject” referred to herein as 3GPP, including: TS 36.300 V15.6.0,“E-UTRA and E-UTRAN Overall Description; Stage 2 (Release 15)”; TR22.886 V16.2.0, “Study on enhancement of 3GPP Support for 5G V2XServices (Release 16)”; TS 23.287 V1.0.0, “Architecture enhancements for5G System (5GS) to support Vehicle-to-Everything (V2X) services (Release16)”; TR 38.885 V16.0.0, “NR; Study on NR Vehicle-to-Everything (V2X)(Release 16)”; 3GPP RAN1 #95 meeting report; 3GPP RAN1 #96bis meetingreport; 3GPP RAN1 #97 meeting report; 3GPP RAN2 #105 meeting report; andR2-1906427, “On HARQ feedback support for groupcast”, Intel Corporation,3GPP RAN2 #106 meeting. The standards and documents listed above arehereby expressly incorporated by reference in their entirety.

FIG. 1 shows a multiple access wireless communication system accordingto one embodiment of the invention. An access network 100 (AN) includesmultiple antenna groups, one including 104 and 106, another including108 and 110, and an additional including 112 and 114. In FIG. 1, onlytwo antennas are shown for each antenna group, however, more or fewerantennas may be utilized for each antenna group. Access terminal 116(AT) is in communication with antennas 112 and 114, where antennas 112and 114 transmit information to access terminal 116 over forward link120 and receive information from access terminal 116 over reverse link118. Access terminal (AT) 122 is in communication with antennas 106 and108, where antennas 106 and 108 transmit information to access terminal(AT) 122 over forward link 126 and receive information from accessterminal (AT) 122 over reverse link 124. In a FDD system, communicationlinks 118, 120, 124 and 126 may use different frequency forcommunication. For example, forward link 120 may use a differentfrequency then that used by reverse link 118.

Each group of antennas and/or the area in which they are designed tocommunicate is often referred to as a sector of the access network. Inthe embodiment, antenna groups each are designed to communicate toaccess terminals in a sector of the areas covered by access network 100.

In communication over forward links 120 and 126, the transmittingantennas of access network 100 may utilize beamforming in order toimprove the signal-to-noise ratio of forward links for the differentaccess terminals 116 and 122. Also, an access network using beamformingto transmit to access terminals scattered randomly through its coveragecauses less interference to access terminals in neighboring cells thanan access network transmitting through a single antenna to all itsaccess terminals.

An access network (AN) may be a fixed station or base station used forcommunicating with the terminals and may also be referred to as anaccess point, a Node B, a base station, an enhanced base station, anevolved Node B (eNB), or some other terminology. An access terminal (AT)may also be called user equipment (UE), a wireless communication device,terminal, access terminal or some other terminology.

FIG. 2 is a simplified block diagram of an embodiment of a transmittersystem 210 (also known as the access network) and a receiver system 250(also known as access terminal (AT) or user equipment (UE)) in a MIMOsystem 200. At the transmitter system 210, traffic data for a number ofdata streams is provided from a data source 212 to a transmit (TX) dataprocessor 214.

In one embodiment, each data stream is transmitted over a respectivetransmit antenna. TX data processor 214 formats, codes, and interleavesthe traffic data for each data stream based on a particular codingscheme selected for that data stream to provide coded data.

The coded data for each data stream may be multiplexed with pilot datausing OFDM techniques. The pilot data is typically a known data patternthat is processed in a known manner and may be used at the receiversystem to estimate the channel response. The multiplexed pilot and codeddata for each data stream is then modulated (i.e., symbol mapped) basedon a particular modulation scheme (e.g., BPSK, QPSK, M-PSK, or M-QAM)selected for that data stream to provide modulation symbols. The datarate, coding, and modulation for each data stream may be determined byinstructions performed by processor 230.

The modulation symbols for all data streams are then provided to a TXMIMO processor 220, which may further process the modulation symbols(e.g., for OFDM). TX MIMO processor 220 then provides N_(T) modulationsymbol streams to N_(T) transmitters (TMTR) 222 a through 222 t. Incertain embodiments, TX MIMO processor 220 applies beamforming weightsto the symbols of the data streams and to the antenna from which thesymbol is being transmitted.

Each transmitter 222 receives and processes a respective symbol streamto provide one or more analog signals, and further conditions (e.g.,amplifies, filters, and upconverts) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. N_(T)modulated signals from transmitters 222 a through 222 t are thentransmitted from N_(T) antennas 224 a through 224 t, respectively.

At receiver system 250, the transmitted modulated signals are receivedby N_(R) antennas 252 a through 252 r and the received signal from eachantenna 252 is provided to a respective receiver (RCVR) 254 a through254 r. Each receiver 254 conditions (e.g., filters, amplifies, anddownconverts) a respective received signal, digitizes the conditionedsignal to provide samples, and further processes the samples to providea corresponding “received” symbol stream.

An RX data processor 260 then receives and processes the N_(R) receivedsymbol streams from N_(R) receivers 254 based on a particular receiverprocessing technique to provide N_(T) “detected” symbol streams. The RXdata processor 260 then demodulates, deinterleaves, and decodes eachdetected symbol stream to recover the traffic data for the data stream.The processing by RX data processor 260 is complementary to thatperformed by TX MIMO processor 220 and TX data processor 214 attransmitter system 210.

A processor 270 periodically determines which pre-coding matrix to use(discussed below). Processor 270 formulates a reverse link messagecomprising a matrix index portion and a rank value portion.

The reverse link message may comprise various types of informationregarding the communication link and/or the received data stream. Thereverse link message is then processed by a TX data processor 238, whichalso receives traffic data for a number of data streams from a datasource 236, modulated by a modulator 280, conditioned by transmitters254 a through 254 r, and transmitted back to transmitter system 210.

At transmitter system 210, the modulated signals from receiver system250 are received by antennas 224, conditioned by receivers 222,demodulated by a demodulator 240, and processed by a RX data processor242 to extract the reserve link message transmitted by the receiversystem 250. Processor 230 then determines which pre-coding matrix to usefor determining the beamforming weights then processes the extractedmessage.

Turning to FIG. 3, this figure shows an alternative simplifiedfunctional block diagram of a communication device according to oneembodiment of the invention. As shown in FIG. 3, the communicationdevice 300 in a wireless communication system can be utilized forrealizing the UEs (or ATs) 116 and 122 in FIG. 1 or the base station (orAN) 100 in FIG. 1, and the wireless communications system is preferablythe LTE or NR system. The communication device 300 may include an inputdevice 302, an output device 304, a control circuit 306, a centralprocessing unit (CPU) 308, a memory 310, a program code 312, and atransceiver 314. The control circuit 306 executes the program code 312in the memory 310 through the CPU 308, thereby controlling an operationof the communications device 300. The communications device 300 canreceive signals input by a user through the input device 302, such as akeyboard or keypad, and can output images and sounds through the outputdevice 304, such as a monitor or speakers. The transceiver 314 is usedto receive and transmit wireless signals, delivering received signals tothe control circuit 306, and outputting signals generated by the controlcircuit 306 wirelessly. The communication device 300 in a wirelesscommunication system can also be utilized for realizing the AN 100 inFIG. 1.

FIG. 4 is a simplified block diagram of the program code 312 shown inFIG. 3 in accordance with one embodiment of the invention. In thisembodiment, the program code 312 includes an application layer 400, aLayer 3 portion 402, and a Layer 2 portion 404, and is coupled to aLayer 1 portion 406. The Layer 3 portion 402 generally performs radioresource control. The Layer 2 portion 404 generally performs linkcontrol. The Layer 1 portion 406 generally performs physicalconnections.

In 3GPP TS 36.300, V2X (Vehicle-to-Everything) service for LTE isintroduced as follows:

23.14 Support for V2X Services

23.14.1 General

Vehicular communication services, represented by V2X services, canconsist of the following four different types: V2V, V21, V2N and V2P, asspecified in TS 22.185 [71].

V2X services can be provided by PC5 interface and/or Uu interface.Support of V2X services via PC5 interface is provided by V2X sidelinkcommunication, which is a mode of communication whereby UEs cancommunicate with each other directly over the PC5 interface, asspecified in TS 23.303 [62]. This communication mode is supported whenthe UE is served by E-UTRAN and when the UE is outside of E-UTRAcoverage. Only the UEs authorised to be used for V2X services canperform V2X sidelink communication.

23.14.1.1 Support for V2X Sidelink Communication

The user plane protocol stack and functions, as specified in subclause23.10.2.1 for sidelink communication, are also used for V2X sidelinkcommunication. In addition, for V2X sidelink communication:

-   -   STCH for sidelink communication is also used for V2X sidelink        communication.    -   Non-V2X (e.g. Public Safety) data is not multiplexed with V2X        data transmitted in resources configured for V2X sidelink        communication.    -   The Access Stratum (AS) is provided with the PPPP and PPPR of a        protocol data unit transmitted over PC5 interface by upper        layers. The packet delay budget (PDB) of the protocol data unit        can be determined from the PPPP. The low PDB is mapped to the        high priority PPPP value (TS 23.285 [72]).    -   The Access Stratum (AS) is provided with a transmit profile (TS        23.285 [72]) of a protocol data unit transmitted over PC5        interface by upper layers.    -   The logical channel prioritization based on PPPP is used for V2X        sidelink communication.

Control plane protocol stack for SBCCH as specified in subclause23.10.2.2 for sidelink communication is also used for V2X sidelinkcommunication.

The UE supporting V2X sidelink communication can operate in two modesfor resource allocation:

-   -   Scheduled resource allocation, characterized by:        -   The UE needs to be RRC_CONNECTED in order to transmit data;        -   The UE requests transmission resources from the eNB. The eNB            schedules transmission resources for transmission of            sidelink control information and data. Sidelink SPS is            supported for scheduled resource allocation;    -   UE autonomous resource selection, characterized by:        -   The UE on its own selects resources from resource pools and            performs transport format selection to transmit sidelink            control information and data;        -   If mapping between the zones and V2X sidelink transmission            resource pools is configured, the UE selects V2X sidelink            resource pool based on the zone UE is located in.        -   The UE performs sensing for (re)selection of sidelink            resources. Based on sensing results, the UE (re)selects some            specific sidelink resources and reserves multiple sidelink            resources. Up to 2 parallel independent resource reservation            processes are allowed to be performed by the UE. The UE is            also allowed to perform a single resource selection for its            V2X sidelink transmission.

In order to assist the eNB to provide sidelink resources, the UE inRRC_CONNECTED may report geographical location information to the eNB.The eNB can configure the UE to report the complete UE geographicallocation information based on periodic reporting via the existingmeasurement report signaling.

Geographical zones can be configured by the eNB or pre-configured. Whenzones are (pre)configured, the world is divided into geographical zonesusing a single fixed reference point (i.e. geographical coordinates (0,0)), length and width. The UE determines the zone identity by means ofmodulo operation using length and width of each zone, number of zones inlength, number of zones in width, the single fixed reference point andthe geographical coordinates of the UE's current location. The lengthand width of each zone, number of zones in length and number of zones inwidth are provided by the eNB when the UE is in coverage andpre-configured when the UE is out of coverage. The zone is configurablefor both in coverage and out of coverage.

For in coverage UE, when the UE uses UE autonomous resource selection,the eNB can provide the mapping between zone(s) and V2X sidelinktransmission resource pools in RRC signalling. For out of coverage UEs,the mapping between the zone(s) and V2X sidelink transmission resourcepools can be pre-configured. If a mapping between zone(s) and V2Xsidelink transmission resource pool is (pre-)configured, the UE selectstransmission sidelink resources from the resource pool corresponding tothe zone where it is currently located. The zone concept is not appliedto exceptional V2X sidelink transmission pools as well as receptionpools. Resource pools for V2X sidelink communication are not configuredbased on priority.

For V2X sidelink transmission, during handover, transmission resourcepool configurations including exceptional transmission resource pool forthe target cell can be signaled in the handover command to reduce thetransmission interruption. In this way, the UE may use the V2X sidelinktransmission resource pools of the target cell before the handover iscompleted as long as either synchronization is performed with the targetcell in case eNB is configured as synchronization source orsynchronization is performed with GNSS in case GNSS is configured assynchronization source. If the exceptional transmission resource pool isincluded in the handover command, the UE uses randomly selectedresources from the exceptional transmission resource pool, starting fromthe reception of handover command. If the UE is configured withscheduled resource allocation in the handover command, the UE continuesto use the exceptional transmission resource pool while the timerassociated with handover is running. If the UE is configured withautonomous resource selection in the target cell the UE continues to usethe exceptional transmission resource pool until the sensing results onthe transmission resource pools for autonomous resource selection areavailable. For exceptional cases (e.g. during RLF, during transitionfrom RRC IDLE to RRC CONNECTED or during change of dedicated V2Xsidelink resource pools within a cell), the UE may select resources inthe exceptional pool provided in serving cell's SIB21 or in dedicatedsignalling based on random selection, and uses them temporarily. Duringcell reselection, the RRC_IDLE UE may use the randomly selectedresources from the exceptional transmission resource pool of thereselected cell until the sensing results on the transmission resourcepools for autonomous resource selection are available.

In order to avoid interruption time in receiving V2X messages due todelay in acquiring reception pools broadcasted from the target cell,synchronisation configuration and reception resource pool configurationfor the target cell can be signaled to RRC_CONNECTED UEs in the handovercommand. For RRC_IDLE UE, it is up to UE implementation to minimize V2Xsidelink transmission/reception interruption time associated withacquisition of SIB21 of the target cell.

A UE is considered in-coverage on the carrier used for V2X sidelinkcommunication whenever it detects a cell on that carrier as per criteriaspecified in TS 36.331 [16]. If the UE that is authorized for V2Xsidelink communication is in-coverage on the frequency used for V2Xsidelink communication or if the eNB provides V2X sidelink configurationfor that frequency (including the case where UE is out of coverage onthat frequency), the UE uses the scheduled resource allocation or UEautonomous resource selection as per eNB configuration. When the UE isout of coverage on the frequency used for V2X sidelink communication andif the eNB does not provide V2X sidelink configuration for thatfrequency, the UE may use a set of transmission and reception resourcepools pre-configured in the UE. V2X sidelink communication resources arenot shared with other non-V2X data transmitted over sidelink.

An RRC_CONNECTED UE may send a Sidelink UE Information message to theserving cell if it is interested in V2X sidelink communicationtransmission in order to request sidelink resources.

If the UE is configured by upper layers to receive V2X sidelinkcommunication and V2X sidelink reception resource pools are provided,the UE receives on those provided resources.

Reception of V2X sidelink communication in different carriers/PLMNs canbe supported by having multiple receiver chains in the UE.

For sidelink SPS, maximum 8 SPS configurations with different parameterscan be configured by eNB and all SPS configurations can be active at thesame time. The activation/deactivation of SPS configuration is signalledvia PDCCH by eNB. The existing logical channel prioritization based onPPPP is used for sidelink SPS.

UE assistance information can be provided to eNB. Reporting of UEassistance information is configured by eNB for V2X sidelinkcommunication. The UE assistance information used for V2X sidelinkcommunication includes traffic characteristic parameters (e.g. a set ofpreferred SPS interval, timing offset with respect to subframe 0 of theSFN 0, PPPP, PPPR, Destination Layer-2 ID, and maximum TB size based onobserved traffic pattern) related to the SPS configuration. The UEassistance information can be reported in case either SPS is alreadyconfigured or not. Triggering of UE assistance information transmissionis left to UE implementation. For instance, the UE is allowed to reportUE assistance information when change in estimated periodicity and/ortiming offset of packet arrival occurs. SR mask per traffic type is notsupported for V2X sidelink communication.

The serving cell can provide synchronization configuration for thecarrier used for V2X sidelink communication. In this case, the UEfollows the synchronization configuration received from serving cell. Incase there is no cell detected on the carrier used for V2X sidelinkcommunication and the UE does not receive synchronization configurationfrom serving cell, the UE follows preconfigured synchronizationconfiguration. There are three types of synchronization reference,namely eNB, UE and GNSS. In case GNSS is configured as synchronizationsource, the UE utilizes the UTC time and (pre)configured DFN offset tocalculate direct frame number and subframe number. In case eNB timing isconfigured as synchronization reference to the UE, for synchronizationand DL measurements, the UE follows the cell associated with theconcerned frequency (when in-coverage on this frequency), or the PCellor the serving cell (when out of coverage on the concerned frequency).UE can indicate the current synchronization reference type it is usingto the eNB. One transmission pool for scheduled resource allocation isconfigured, taking into account the synchronization reference of the UE.

For controlling channel utilization, the network is able to indicate howthe UE adapts its transmission parameters for each transmission pooldepending on the Channel Busy Ratio (CBR). The UE measures all theconfigured transmission pools including exceptional pool. If a pool is(pre)configured such that a UE shall always transmit PSCCH and PSSCH inadjacent resource blocks the UE measures PSCCH and PSSCH resourcestogether. If a pool is (pre)configured such that a UE may transmit PSCCHand the corresponding PSSCH in non-adjacent resource blocks in asubframe then PSSCH pool and PSCCH pool are measured separately.

A UE in RRC_CONNECTED can be configured to report CBR measurementresults. For CBR reporting, periodic reporting and event triggeredreporting are supported. Two reporting events are introduced forevent-triggered CBR reporting. In case PSSCH and PSCCH resources areplaced non-adjacently, only PSSCH pool measurement is used forevent-triggered CBR reporting. In case PSSCH and PSCCH resources areplaced adjacently, CBR measurement of both the PSSCH and PSCCH resourcesis used for event-triggered CBR reporting. Event-triggered CBR reportingis triggered by overloaded threshold and/or less-loaded threshold. Thenetwork can configure which of the transmission pools the UE needs toreport.

A UE (regardless of its RRC state) performs transmission parameteradaptation based on the CBR. In case PSSCH and PSCCH resources areplaced non-adjacently, only PSSCH pool measurement is used fortransmission parameter adaptation. In case PSSCH and PSCCH resources areplaced adjacently, CBR measurement of both the PSSCH and PSCCH resourcesis used for transmission parameter adaptation. When CBR measurements arenot available, the default transmission parameters are used. Theexemplary adapted transmission parameters include maximum transmissionpower, range of the number of retransmission per TB, range of PSSCH RBnumber, range of MCS, maximum limit on channel occupancy ratio. Thetransmission parameter adaption applies to all transmission poolsincluding exceptional pool.

A UE using scheduled resource allocation may be configured to performsensing and report the sensing result. The UE performs sensing only inthe V2X sidelink transmission resource pool(s) for which sensing resultis configured to be reported. Only periodic reporting is supported.

For V2X sidelink communication, sidelink transmission and/or receptionresources including exceptional pool for different frequencies forscheduled resource allocation and UE autonomous resource selection maybe provided. The sidelink resources for different frequencies can beprovided via dedicated signalling, SIB21 and/or preconfiguration. Theserving cell may indicate to the UE only the frequency on which the UEmay acquire the resource configuration for V2X sidelink communication.If multiple frequencies and associated resource information areprovided, it is up to UE implementation to select the frequency amongthe provided frequencies. The UE shall not use preconfiguredtransmission resource if the UE detects a cell providing resourceconfiguration or inter-carrier resource configuration for V2X sidelinkcommunication. Frequencies which may provide V2X sidelink communicationresource configuration or cross-carrier configuration can be signalledin SIB21 or pre-configured in the UE. The RRC_IDLE UE may prioritize thefrequency that provides cross-carrier resource configuration for V2Xsidelink communication during cell reselection.

If the UE supports multiple transmission chains, it may simultaneouslytransmit on multiple carriers via PC5. For the case where multiplefrequencies for V2X are supported, a mapping between V2X service typesand V2X frequencies is configured by upper layers. The UE should ensurea V2X service to be transmitted on the corresponding frequency. Forscheduled resource allocation, the eNB can schedule a V2X transmissionon a frequency based on the Sidelink BSR, as specified in TS 36.321[13], in which the UE includes the Destination Index uniquely associatedwith a frequency reported by the UE to the eNB in Sidelink UEInformation message as specified in TS 36.331 [16].

Carrier aggregation (CA) in sidelink is supported for V2X sidelinkcommunication. It applies to both in coverage UEs and out of coverageUEs. For CA in sidelink, neither primary component carrier nor secondarycomponent carriers are defined. Each resource pool (pre)configured forV2X sidelink communication transmission or reception is associated to asingle carrier. When a UE supporting CA in sidelink uses autonomousresource selection, it performs carrier selection and may select one ormore carriers used for V2X sidelink communication transmission. Thecarrier selection is performed at MAC layer, depending on the CBR of the(pre)configured carriers for V2X sidelink communication and the PPPP(s)of the V2X messages to be transmitted. The carrier reselection may beperformed when resource reselection is triggered and is triggered foreach sidelink process. In order to avoid frequent switching acrossdifferent carriers, the UE may keep using a carrier already selected fortransmission, if the measured CBR on this carrier is lower than a(pre)configured threshold. All selected carriers should have the samesynchronization reference or the same synchronization priorityconfiguration. For a UE using autonomous resource selection, logicalchannel prioritization is performed for a sidelink resource on a carrierdepending on the CBR measured on the carrier and the PPPP of thesidelink logical channels as specified in TS 36.321 [13].

Sidelink packet duplication is supported for V2X sidelink communicationand is performed at PDCP layer of the UE. For sidelink packetduplication for transmission, a PDCP PDU is duplicated at the PDCPentity. The duplicated PDCP PDUs of the same PDCP entity are submittedto two different RLC entities and associated to two different sidelinklogical channels respectively. The duplicated PDCP PDUs of the same PDCPentity are only allowed to be transmitted on different sidelinkcarriers. A UE can activate or deactivate sidelink packet duplicationbased on (pre)configuration. Sidelink packet duplication does not applyto transmission with Rel-14 transmit profile (TS 23.285 [72]). The PPPRvalue(s) for which sidelink packet duplication is supported can be(pre)configured via a PPPR threshold. For UE autonomous resourceselection and scheduled resource allocation, the UE shall performsidelink packet duplication for the data with the configured PPPRvalue(s) until packet duplication is deconfigured for these PPPRvalue(s). For scheduled resource allocation, the UE reports the amountof data associated with one or more PPPR values, and the destination(s)to which the data belongs via sidelink BSR(s). A mapping of PPPR valuesto logical channel groups can be configured by the eNB, and the PPPRvalue(s) are reflected by the associated logical channel group IDincluded in the sidelink BSR(s). A list of PPPR value(s) may be reportedin Sidelink UE information by an RRC_CONNECTED UE.

For a UE using scheduled resource allocation, two non-overlapped sets ofcarriers are configured by the eNB per Destination reported by the UE tothe network, and they apply to all the PPPR(s) that are configured forsidelink packet duplication. The UE then associates two duplicatedsidelink logical channels corresponding to the same PDCP entityrespectively with the two sets of carriers configured for theDestination of the two sidelink logical channels. The associationbetween the duplicated sidelink logical channel and the carrier set isup to UE implementation. Data of a duplicated sidelink logical channelcan only be transmitted on the carrier(s) in the associated carrier set.

For V2X sidelink communication reception, packet duplication detectionis performed at PDCP layer of the UE. Reordering function is alsosupported at PDCP layer and how to set the reordering timer at the PDCPlayer is up to UE implementation. There are specific logical channelidentities which apply to the sidelink logical channel used for sidelinkpacket duplication exclusively as specified in TS 36.321 [13].

The UE may receive the V2X sidelink communication of other PLMNs. Theserving cell can indicate to the UE the resource configuration for V2Xsidelink communication reception for inter-PLMN operation directly oronly the frequency on which the UE may acquire the inter-PLMN resourceconfiguration for V2X sidelink communication reception. V2X sidelinkcommunication transmission in other PLMNs is not allowed.

When UL transmission overlaps in time domain with V2X sidelinktransmission in the same frequency, the UE prioritizes the V2X sidelinktransmission over the UL transmission if the PPPP of sidelink MAC PDU islower than a (pre)configured PPPP threshold; otherwise, the UEprioritizes the UL transmission over the V2X sidelink transmission. WhenUL transmission overlaps in time domain with V2X sidelink transmissionin different frequency, the UE may prioritize the V2X sidelinktransmission over the UL transmission or reduce UL transmission power ifthe PPPP of sidelink MAC PDU is lower than a (pre)configured PPPPthreshold; otherwise, the UE prioritizes the UL transmission over theV2X sidelink transmission or reduces V2X sidelink transmission power.However, if UL transmission is prioritized by upper layer as specifiedin TS 24.386 [75] or random access procedure is performed, the UEprioritizes UL transmission over any V2X sidelink transmission (i.e.irrespectively of the sidelink MAC PDU's PPPP).

Resource pool for transmission of pedestrian UE (P-UE) may be overlappedwith resources for V2X sidelink communication. For each transmissionpool, resource selection mechanism (i.e. random selection, partialsensing based selection or either random selection or partial sensingbased selection), which is allowed to be used in this pool, is alsoconfigured. If P-UE is configured to use either random selection orpartial sensing based selection for one transmission pool, it is up toUE implementation to select a specific resource selection mechanism. Ifthe P-UE is configured to use partial sensing based selection only, theP-UE shall use partial sensing based selection in the pool. The P-UEshall not do random selection in the pool wherein only partial sensingis allowed. If the eNB does not provide a random selection pool, theP-UEs that support only random selection cannot perform sidelinktransmission. In exceptional pool, the P-UE uses random selection. TheP-UE can send Sidelink UE Information message to indicate that itrequests resource pools for P2X-related V2X sidelink communicationtransmission as specified in TS 36.331 [16].

It is not mandatory for P-UE to support zone based resource selection.The P-UE reports whether it supports zone based resource selection aspart of UE capability signalling. If the P-UE supports zone basedresource selection, the network can provide zone based configuration viaonly dedicated signalling.

Power saving of P-UE can be achieved by UE implementation and upperlayer mechanisms. P-UE does not perform CBR measurement. However, P-UEadjusts the transmission parameters based on the default transmissionparameter configuration, which can be provided to the P-UE via RRCsignalling.

To support the co-existence of CEN DSRC and V2X sidelink communication,the upper layers of the UE which is performing V2X sidelinkcommunication send an indication to lower layers when the UE is withinthe proximity of CEN DSRC tolling station(s).

23.14.1.2 Support for V2X Communication Via Uu

For V2X communication in uplink, maximum 8 SPS configurations withdifferent parameters can be configured by eNB and all SPS configurationscan be active at the same time. The activation/deactivation of each SPSconfiguration is signalled via PDCCH by eNB. The existing logicalchannel prioritization for Uu is used.

For V2X communication, UE assistance information can be provided to eNB.Reporting of UE assistance information is configured by eNB. The UEassistance information includes parameters (e.g. a set of preferred SPSinterval, timing offset with respect to subframe 0 of the SFN 0, LCIDand maximum TB size based on observed traffic pattern) related to theSPS configuration. Triggering of UE assistance information transmissionis left to UE implementation. For instance, the UE is allowed to reportthe UE assistance information when change in estimated periodicityand/or timing offset of packet arrival occurs. For V2X communication viaUu, SR mask as per legacy mechanism can be used.

For unicast transmission of V2X messages, the V2X message can bedelivered via Non-GBR bearers as well as GBR bearers. In order to meetthe QoS requirements for V2X message delivery for V2X services, aNon-GBR QCI value and a GBR QCI value for V2X messages are used asspecified in TS 23.285 [72].

For broadcasting V2X messages, SC-PTM or MBSFN transmission can be used.In order to reduce SC-PTM/MBSFN latency, shorter (SC-)MCCH repetitionperiod for SC-PTM/MBSFN, modification period for SC-PTM/MBSFN and MCHscheduling period for MBSFN are supported. Reception of downlinkbroadcast of V2X messages in different carriers/PLMNs can be supportedby having multiple receiver chains in the UE. A GBR QCI value is usedfor the delivery of V2X messages over MBMS bearers as specified in TS23.285 [72].

In 3GPP TR 22.886, vehicle platooning with a leader vehicle isintroduced in 5G V2X as follows:

5.1 eV2X Support for Vehicle Platooning

5.1.1 Description

Platooning is operating a group of vehicles in a closely linked mannerso that the vehicles move like a train with virtual strings attachedbetween vehicles. To maintain distance between vehicles, the vehiclesneeds to share status information such as speed, heading and intentionssuch as braking, acceleration, etc. By use of platooning, the distancesbetween vehicles can be reduced, overall fuel consumption is lowered,and the number of needed drivers can be reduced.

Following aspects need to be supported for platooning.

Join/Leave

To form a platoon, vehicles need to exchange intent such as interest toform a platoon, intention to be a leader or follower of the platoon. Andwhen a vehicle reaches a destination or has to leave the platoon, thisintent should be also exchanged among vehicles of the platoon. Thisexchange of intent can occur at any time while the platoon is active.

Announcement/Warning

When a platoon is formed and operational, a vehicle which do not belongto the platoon should aware the existence of the platoon. Otherwise, thevehicle may move into the middle of the platoon and disrupt theoperation of the platoon. Thus, the platoon should be known to othervehicles beyond the communication range among vehicles of the sameplatoon.

Group Communication

There are several messages that are exchanged for platoon management.E.g., vehicles of the platoon need to exchange information regardingwhen to take which road, whether to brake or accelerate and when, etc.At least, 30 CAM messages/seconds needs to be supported. [3]. Inaddition, the lead vehicle consume more fuel than other vehicles,sometime lead vehicle may request next vehicle to be a leader. This kindof communication can be done between the two vehicles without othervehicles' involvement.

To prevent potential security threats such as revealing of the route,these messages should be supported with confidentiality and bedeciphered only by the vehicles of the platoon. In addition, due to theprivate nature of the messages, the communication range of thesemessages is from the lead vehicle to the last vehicle of the platoon,and typically line-of-sight. Because the size of the platoon can differeven on the move, resource-efficient distribution of messages forplatooning and dynamic control of the distribution area of the messagesshould be supported.

Two sets of Platooning performances requirements are supported:

-   -   Set 1: According to [11][2], the distance between vehicles for        normal density platooning may be larger than 2 meters. When the        platoon moves at 100 km/h, vehicles move 1 meter in 36 ms.        Considering the round-trip-time and processing delay, message        transmission frequency up to 40 Hz, translating into 25 ms radio        latency with message sizes of around 300-400 bytes should be        supported.    -   Set 2: According to [2], the distance between vehicles for high        density platooning is 1 meter. When the platoon moves at 100        km/h, vehicles move 1 meter in 36 ms. Considering        round-trip-time and processing delay, message transmission        frequency up to 100 Hz, translating into at least 10 ms latency        with message sizes of around 50-1200 bytes should be supported.

If the platoon is too long, it will sometimes interrupt the operation ofother vehicles and traffic management authority. So, there should belimit on how many vehicles can be included in a platoon. This isespecially true considering that a truck can span more than 15 m.

In 3GPP TS 23.287, the architecture for NR V2X is introduced as follows:

4 Architecture Model and Concepts

4.1 General Concept

There are two modes of operation for V2X communication, namely V2Xcommunication over PC5 reference point and V2X communication over Uureference point. These two operation modes may be used by a UEindependently for transmission and reception.

V2X communications over PC5 reference point are supported by LTE and/orNR.

V2X communications over Uu reference point are supported by E-UTRAconnected to 5GC and/or NR connected to 5GC. In this release, V2Xcommunication over Uu reference point is only unicast.

4.2 Architectural Reference Model

4.2.1 PC5 and Uu Based V2X Architecture Reference Model

4.2.1.1 Non-Roaming 5G System Architecture for V2X Communication OverPC5 and Uu Reference Points

FIG. 4.2.1.1-1 shows the high level view of the non-roaming 5G Systemarchitecture for V2X communication over PC5 and Uu reference points.

[FIG. 4.2.1.1-1 of 3GPP TS 23.287 V1.0.0, Entitled “Non-Roaming 5GSystem Architecture for V2X Communication Over PC5 and Uu ReferencePoints”, is Reproduced as FIG. 5]

Furthermore, in 3GPP TS 23.287, identifiers for NR V2X communication areintroduced are as follows:

5.6 Identifiers

5.6.1 Identifiers for V2X Communication Over PC5 Reference Point

5.6.1.1 General

Each UE has one or more Layer-2 IDs for V2X communication over PC5reference point, consisting of:

-   -   Source Layer-2 ID(s); and    -   Destination Layer-2 ID(s).

Source and destination Layer-2 IDs are included in layer-2 frames senton the layer-2 link of the PC5 reference point identifying the layer-2source and destination of these frames. Source Layer-2 IDs are alwaysself-assigned by the UE originating the corresponding layer-2 frames.

The selection of the source and destination Layer-2 ID(s) by a UEdepends on the communication mode of V2X communication over PC5reference point for this layer-2 link, as described in clauses 5.6.1.2,5.6.1.3, and 5.6.1.4. The source Layer-2 IDs may differ betweendifferent communication modes.

When P-based V2X communication is supported, the UE configures a linklocal IPv6 address to be used as the source IP address, as defined inclause 4.5.3 of TS 23.303 [17]. The UE may use this IP address for V2Xcommunication over PC5 reference point without sending NeighbourSolicitation and Neighbour Advertisement message for Duplicate AddressDetection.

If the UE has an active V2X application that requires privacy support inthe current Geographical Area, as identified by configuration describedin clause 5.1.2.1, in order to ensure that a source UE (e.g. vehicle)cannot be tracked or identified by any other UEs (e.g. vehicles) beyonda certain short time-period required by the application, the sourceLayer-2 ID shall be changed over time and shall be randomized. ForIP-based V2X communication over PC5 reference point, the source IPaddress shall also be changed overtime and shall be randomized. Thechange of the identifiers of a source UE must be synchronized acrosslayers used for PC5, e.g. when the application layer identifier changes,the source Layer-2 ID and the source IP address need to be changed.

5.6.1.2 Identifiers for Broadcast Mode V2X Communication Over PC5Reference Point

For broadcast mode of V2X communication over PC5 reference point, the UEis configured with the destination Layer-2 ID(s) to be used for V2Xservices. The destination Layer-2 ID for a V2X communication is selectedbased on the configuration as described in clause 5.1.2.1.

The UE self-selects a source Layer-2 ID. The UE may use different sourceLayer-2 IDs for different types of PC5 reference points, i.e. LTE basedPC5 and NR based PC5.

5.6.1.3 Identifiers for Groupcast Mode V2X Communication Over PC5Reference Point

For groupcast mode of V2X communication over PC5 reference point, theV2X application layer may provide group identifier information. When thegroup identifier information is provided by the V2X application layer,the UE converts the provided group identifier into a destination Layer-2ID. When the group identifier information is not provided by the V2Xapplication layer, the UE determines the destination Layer-2 ID based onconfiguration of the mapping between service type (e.g. PSID/ITS-AID)and Layer-2 ID, as specified in clause 5.1.2.1.

-   NOTE: The mechanism for converting the V2X application layer    provided group identifier to the destination Layer-2 ID is defined    in Stage 3.

The UE self-selects a source Layer-2 ID.

-   Editor's note: Further updates of the identifiers description may be    required based on RAN WG feedback.    5.6.1.4 Identifiers for Unicast Mode V2X Communication Over PC5    Reference Point

For unicast mode of V2X communication over PC5 reference point, thedestination Layer-2 ID used depends on the communication peer, which isdiscovered during the establishment of the unicast link. The initialsignalling for the establishment of the unicast link may use a defaultdestination Layer-2 ID associated with the service type (e.g.PSID/ITS-AID) configured for unicast link establishment, as specified inclause 5.1.2.1. During the unicast link establishment procedure, Layer-2IDs are exchanged, and should be used for future communication betweenthe two UEs, as specified in clause 6.3.3.1.

The Application Layer ID is associated with one or more V2X applicationswithin the UE. If UE has more than one Application Layer IDs, eachApplication Layer ID of the same UE may be seen as different UE'sApplication Layer ID from the peer UE's perspective.

The UE needs to maintain a mapping between the Application Layer IDs andthe source Layer-2 IDs used for the unicast links, as the V2Xapplication layer does not use the Layer-2 IDs. This allows the changeof source Layer-2 ID without interrupting the V2X applications.

When Application Layer IDs change, the source Layer-2 ID(s) of theunicast link(s) shall be changed if the link(s) was used for V2Xcommunication with the changed Application Layer IDs.

A UE may establish multiple unicast links with a peer UE and use thesame or different source Layer-2 IDs for these unicast links.

6.3.2 Groupcast Mode V2X Communication Over PC5 Reference Point

To perform groupcast mode of V2X communication over PC5 reference point,the UE is configured with the related information as described in clause5.1.2.1.

FIG. 6.3.2-1 shows the procedure for groupcast mode of V2X communicationover PC5 reference point.

[FIG. 6.3.2-1 of 3GPP TS 23.287 V1.0.0, Entitled “Procedure forGroupcast Mode of V2X Communication Over PC5 Reference Point”, isReproduced as FIG. 6]

-   -   1. V2X group management is carried out by the V2X application        layer and is out of scope of this specification.    -   2. The V2X application layer may provide group identifier        information (i.e. an Application-layer V2X Group identifier) as        specified in clause 5.6.1.3.        -   The V2X application layer may provide service requirements            for this communication.    -   3. Transmitting UE determines a source Layer-2 ID and a        destination Layer-2 ID and Receiving UE(s) determine destination        Layer-2 ID, as specified in clauses 5.6.1.1 and 5.6.1.3.        -   The destination Layer-2 ID is passed down to the AS layer of            Receiving UE(s) for the group communication reception.        -   Transmitting UE determines the PC5 QoS parameters for this            groupcast as specified in clauses 5.4.1.1 and 5.4.1.3.    -   4. Transmitting UE has a V2X service associated with this group        communication.        -   Transmitting UE sends the V2X service data using the source            Layer-2 ID and the destination Layer-2 ID.    -   NOTE: In step 4, there is only one groupcast message from the        transmitting UE

In 3GPP TR 38.885, a NR sidelink unicast, groupcast, and broadcastdesign is introduced as follows:

5 Sidelink (PC5) Aspects

5.1 NR Sidelink Unicast, Groupcast, and Broadcast Design

SL broadcast, groupcast, and unicast transmissions are supported for thein-coverage, out-of-coverage and partial-coverage scenarios.

The AS protocol stack for the control plane in the PC5 interfaceconsists of at least RRC, PDCP, RLC and MAC sublayers, and the physicallayer. The protocol stack of PC5-C is shown in FIGS. 5.1-1.

[FIGS. 5.1-1 of 3GPP TR 38.885 V16.0.0, Entitled “PC5 Control Plane(PC5-C) Protocol Stack”, is Reproduced as FIG. 7]

The AS protocol stack for user plane in the PC5 interface consists ofSDAP, PDCP, RLC and MAC sublayers, and the physical layer. The protocolstack of PC5-U is shown in FIGS. 5.1-2.

[FIGS. 5.1-2 of 3GPP TR 38.885 V16.0.0, Entitled “PC5 User Plane (PC5-U)Protocol Stack”, is Reproduced as FIG. 8].

For the purposes of physical layer analysis, it is assumed that higherlayers decide if unicast, groupcast, or broadcast transmission is to beused for a particular data transfer, and they correspondingly inform thephysical layer. When considering a unicast or groupcast transmission, itis assumed that the UE is able to establish which unicast or groupcastsession a transmission belongs to, and that the following information isknown to the physical layer:

-   -   Identities:        -   The layer-1 source and destination IDs, conveyed in SCI        -   Additional layer-1ID(s), conveyed via PSCCH, at least for            the purpose of identifying which transmissions can be            combined in reception when HARQ feedback is in use (see            Section 5.1.2.2)        -   HARQ process ID

For the purpose of Layer 2 analysis, it is assumed that upper layers(i.e. above AS) provide the information on whether it is a unicast,groupcast or broadcast transmission for a particular data transfer. Forthe unicast and groupcast transmission in SL, the following informationis known to Layer 2:

-   -   Identities:        -   Unicast: destination ID, source ID        -   Groupcast: destination Group ID, source ID

Any UE configured to receive a group destination Layer 2 ID is allowedto receive the groupcast transmission, whether it is within or beyondthe “minimum communication range” provided by upper layers.

For AS-level link management in unicast, SL RLM/RLF declaration issupported. For RLC AM in SL unicast, RLF declaration is triggered byindication from RLC that the maximum number of retransmissions has beenreached. The AS-level link status (e.g., failure) should be informed toupper layers. No RLM design specific to groupcast, different than theRLM procedure for unicast, is considered. There is no need for RLM/RLFdeclarations among group members for groupcast.

Discovery procedure and related messages for unicast and groupcasttransmission are up to upper layers.

5.1.1 Physical Layer Structures

In this section, the design of a physical SL control channel (PSCCH), aphysical SL shared channel (PSSCH), a physical SL feedback channel(PSFCH) and other matters related to physical layer structures arestudied. In addition to what is discussed in this TR, at least aspectsrelated to modulation, scrambling, RE mapping and rate matching would beincluded in normative work. For design of the physical SL broadcastchannel (PSBCH), refer to Section 5.2.

The waveform supported in the study is CP-OFDM.

5.1.1.1 Subcarrier Spacing and Cyclic Prefix

In FR1, 15 kHz, 30 kHz and 60 kHz SCS are supported with normal CP, and60 kHz SCS with extended CP. In FR2, 60 kHz and 120 kHz SCS aresupported with normal CP, and 60 kHz SCS with extended CP. In a givencarrier, a UE is not required to receive simultaneously SL transmissionswith more than one combination of SCS and CP, nor transmitsimultaneously SL transmissions with more than one combination of SCSand CP. The numerology configuration is part of the SL BWP configuration(see Section 5.1.1.3).

5.1.1.2 Channel Coding

The channel coding defined for data and control in NR Uu arerespectively the starting points for data and control on the NR SL.

5.1.1.3 SL Bandwidth Parts and Resource Pools

BWP is defined for SL, and the same SL BWP is used for transmission andreception. In specification terms, in a licensed carrier, SL BWP wouldbe defined separately, and have separate configuration signalling, fromUu BWP. One SL BWP is (pre-)configured for RRC IDLE and out-of-coverageNR V2X UEs in a carrier. For UEs in RRC_CONNECTED mode, one SL BWP isactive in a carrier. No signalling is exchanged over SL for theactivation or deactivation of a SL BWP.

In a carrier, only one SL BWP is configured for a UE, and the UE is notexpected to use at the same time a different numerology in the SL BWPthan an active UL BWP.

A resource pool is a set of time-frequency resources that can be usedfor SL transmission and/or reception. From the UE point of view, aresource pool is inside the UE's bandwidth, within a SL BWP and has asingle numerology. Time domain resources in a resource pool can benon-contiguous. Multiple resource pools can be (pre-)configured to a UEin a carrier.

5.1.1.4 Resource Arrangements

NR V2X may be deployed in a carrier dedicated to ITS services, or acarrier shared with cellular services. Therefore, resource arrangementswhere all the symbols in a slot are available for SL, and where only asubset of consecutive symbols in a slot (which are not dynamicallyindicated) are available for SL are supported. The latter case is notintended for use in ITS spectrum, if normative specification work doesnot find a forward compatibility issue.

Resource allocation for PSSCH is based on the concept of sub-channels inthe frequency domain, and a UE performs either transmission or receptionin a slot on a carrier. Blind retransmissions of a TB are supported, andresource allocation Mode 2 (see section 5.3.1) supports reservation ofSL resources at least for such blind retransmission.

PSFCH (see section 5.1.2.2) supports at least a format which uses thelast symbol(s) available for SL in a slot.

5.1.1.5 Reference Signals

DM-RS associated with PSSCH are transmitted in one of several possiblepatterns in the time domain. In FR2, a PT-RS for PSSCH is alsosupported.

Other candidate reference signals are: CSI-RS (see section 5.1.2.3 forCSI procedure), SRS, and AGC training signal.

5.1.2 Physical Layer Procedures

In this section, physical layer procedures are studied. For proceduresrelated to SL synchronization, refer to Section 5.2

5.1.2.1 Multiplexing of Physical Channels

For the purposes of this section, a PSSCH is said to be “associated” toa PSCCH when the PSCCH carries at least the SCI necessary to decode thePSSCH. The following options for multiplexing of a PSCCH and associatedPSSCH are studied:

Option 1: PSCCH and the associated PSSCH are transmitted usingnon-overlapping time resources.

-   -   Option 1A: The frequency resources used by the two channels are        the same.    -   Option 1B: The frequency resources used by the two channels can        be different.

Option 2: PSCCH and the associated PSSCH are transmitted usingnon-overlapping frequency resources in the all the time resources usedfor transmission. The time resources used by the two channels are thesame.

Option 3: Part of PSCCH and the associated PSSCH are transmitted usingoverlapping time resources in non-overlapping frequency resources, butanother part of the associated PSSCH and/or another part of the PSCCHare transmitted using non-overlapping time resources.

Of the options described above, at least Option 3 is supported.(Editor's note: this is a RAN1 working assumption).

5.1.2.2 HARQ Procedures

5.1.2.2.1 General HARQ Procedure

For SL unicast and groupcast, HARQ feedback and HARQ combining in thephysical layer are supported. HARQ-ACK feedback for a PSSCH is carriedin SFCI format(s) via PSFCH in resource allocation Modes 1 and 2.

When SL HARQ feedback is enabled for unicast, in the case of non-CBGoperation the receiver UE generates HARQ-ACK if it successfully decodesthe corresponding TB. It generates HARQ-NACK if it does not successfullydecode the corresponding TB after decoding the associated PSCCH targetedto the receiver UE.

When SL HARQ feedback is enabled for groupcast, it is supported to useTX-RX distance and/or RSRP in deciding whether to send HARQ feedback. Inthe case of non-CBG operation, two options are supported: (Editor'snote: This is a RAN1 working assumption)

Option 1: Receiver UE transmits HARQ-NACK on PSFCH if it fails to decodethe corresponding TB after decoding the associated PSCCH. It transmitsno signal on PSFCH otherwise.

Option 2: Receiver UE transmits HARQ-ACK on PSFCH if it successfullydecodes the corresponding TB. It transmits HARQ-NACK on PSFCH if it doesnot successfully decode the corresponding TB after decoding theassociated PSCCH which targets the receiver UE.

5.1.2.2.2 HARQ procedure details for Mode 1 resource allocation

The time between PSSCH and sending HARQ feedback on PSFCH is(pre-)configured. For unicast and groupcast, if retransmission is neededon the SL, this can be indicated to the gNB by an in-coverage UE usingPUCCH. It is supported that the transmitter UE sends the indication toits serving gNB in a form such as SR/BSR, but not in the form of HARQACK/NACK.

The study considered an additional option of the receiver UE sending theindication to its serving gNB, as HARQ ACK/NACK, and assuming nointer-BS communication.

SL re-transmission resources can also be scheduled by the gNB withoutreceiving such an indication.

5.1.2.2.3 HARQ Procedure Details for Mode 2 Resource Allocation

The time between PSSCH and sending HARQ feedback on PSFCH is(pre-)configured.

In 3GPP RAN1 #95 meeting [5], some agreements have been made about NRV2X.

Agreements:

-   -   Physical sidelink feedback channel (PSFCH) is defined and it is        supported to convey SFCI for unicast and groupcast via PSFCH.        Agreements:    -   When SL HARQ feedback is enabled for unicast, the following        operation is supported for the non-CBG case:    -   Receiver UE generates HARQ-ACK if it successfully decodes the        corresponding TB. It generates HARQ-NACK if it does not        successfully decode the corresponding TB after decoding the        associated PSCCH which targets the receiver UE.    -   FFS whether to support SL HARQ feedback per CBG

Agreements:

-   -   When SL HARQ feedback is enabled for groupcast, the following        operations are further studied for the non-CBG case:        -   Option 1: Receiver UE transmits HARQ-NACK on PSFCH if it            fails to decode the corresponding TB after decoding the            associated PSCCH. It transmits no signal on PSFCH otherwise.            Details are FFS including the following:            -   Whether to introduce an additional criterion in deciding                HARQ-NACK transmission            -   Whether/how to handle DTX issue (i.e., transmitter UE                cannot recognize the case that a receiver UE misses                PSCCH scheduling PSSCH)            -   Issues when multiple receiver UEs transmit HARQ-NACK on                the same resource                -   How to determine the presence of HARQ-NACK                    transmissions from receiver UEs                -   Whether/how to handle destructive channel sum effect                    of HARQ-NACK transmissions from multiple receiver                    UEs if the same signal is used        -   Option 2: Receiver UE transmits HARQ-ACK on PSFCH if it            successfully decodes the corresponding TB. It transmits            HARQ-NACK on PSFCH if it does not successfully decode the            corresponding TB after decoding the associated PSCCH which            targets the receiver UE. Details are FFS including the            following:            -   Whether to introduce an additional criterion in deciding                HARQ-ACK/NACK transmission            -   How to determine the PSFCH resource used by each                receiver UE        -   FFS whether to support SL HARQ feedback per CBG        -   Other options are not precluded

Agreements:

-   -   It is supported to enable and disable SL HARQ feedback in        unicast and groupcast.        -   FFS when HARQ feedback is enabled and disabled.

Agreements:

-   -   Study further whether to support UE sending to gNB information        which may trigger scheduling retransmission resource in mode 1.        FFS including        -   Which information to send        -   Which UE to send to gNB        -   Which channel to use        -   Which resource to use

In the 3GPP RAN1 #96bis meeting (as captured in the 3GPP RAN1 #96bismeeting report), it is further discussed whether receiver UEs in a samegroup share a PSFCH (Physical Sidelink Feedback Channel) or use aseparate PSFCH for HARQ ACK (Hybrid Automatic Repeat RequestAcknowledgement)/NACK (Negative Acknowledgement) associated withgroupcast transmission as follows:

Agreements:

-   -   In HARQ feedback for groupcast,        -   When Option 1 is used for a groupcast transmission, it is            supported            -   all the receiver UEs share a PSFCH            -   FFS: a subset of the receiver UEs share a PSFCH            -   FFS: all or a subset of receiver UEs share a pool of                PSFCH.        -   When Option 2 is used for a groupcast transmission, it is            supported            -   each receiver UE uses a separate PSFCH for HARQ                ACK/NACK.            -   FFS: all or a subset of receiver UEs share a PSFCH for                ACK transmission and another PSFCH for NACK transmission        -   FFS on which entity and how to allocate PSFCH resource to            the receiver UE(s)        -   FFS whether or not to additionally support a mixture of            option 1 and option 2 for a groupcast transmission    -   Note: Each PSFCH is mapped to a time, frequency, and code        resource.

In the 3GPP RAN1 #97 meeting (as captured in the 3GPP RAN1 #97 meetingreport), it was agreed that an implicit mechanism as follows:

Agreements:

-   -   At least for the case when the PSFCH in a slot is in response to        a single PSSCH:        -   Implicit mechanism is used to determine at least frequency            and/or code domain resource of PSFCH, within a configured            resource pool. At least the following parameters are used in            the implicit mechanism:            -   Slot index (FFS details) associated with                PSCCH/PSSCH/PSFCH            -   Sub-channel(s) (FFS details) associated with PSCCH/PSSCH            -   Identifier (FFS details) to distinguish each RX UE in a                group for Option 2 groupcast HARQ feedback            -   FFS detailed applicability of the above parameters            -   FFS: Other parameters (e.g. SL-RSRP/SINR, Layer-1 source                ID, location information, etc.)

In the 3GPP RAN2 #105 meeting (as captured in the 3GPP RAN2 #105 meetingreport), it was discussed whether leader vehicle is visible in the AS(Access Stratum) layer as follows:

-   R2-1901730 Summary Report of [104 #60][NR/V2X] Groupcast (Qualcomm)    Qualcomm Incorporatd discussion FS_NR_V2X    -   Proposal 4: Whether the design need to support platoon leader        being visible in AS layer depends on RAN1 progress    -   We need to wait for RAN1 progress/decision on the resource        allocation mechanism first.

In the 3GPP RAN2 #106 meeting (as captured in 3GPP R2-1906427), severalsolutions were discussed regarding feedback resource allocation forgroupcast (option 2) as follows:

Option 2:

For the case of option 2, the situation is a bit tricky since both ACKsand NACKs can be transmitted and each RX UE may need to be allocated aseparate ACK/NACK resource. In other words, we can view the PSFCHtransmissions for UE within the group as multiple unicast feedbacks tobe multiplexed. In this case, we can consider the following threealternatives:

-   -   1) The TX UE has to allocate specific resources based on unique        group-wide identifiers for the intended recipients for its data        transmission in order to determine whether or not the TB(s)        is/are successfully decoded. This requires some indication from        the upper layers regarding at least the destination L2 IDs for        other members of the group.    -   2) Another alternative is for the group leader to assume the        responsibility of managing HARQ related ID allocation for the        entire group. Since the target use case is platooning, we assume        that the group leader is already known to the group members and        is not expected to change very dynamically.    -   3) A final option can be to consider the gNB as the AS layer        entity responsible for performing the mapping between L2        Destination ID and HARQ identifier. However, in our view, this        option is relevant for the case when in connected mode and the        group leader might have to assume this responsibility otherwise        in any case.

One or multiple of following terminologies may be used hereafter:

-   -   BS: A network central unit or a network node in NR which is used        to control one or multiple TRPs which are associated with one or        multiple cells. Communication between BS and TRP(s) is via        fronthaul. BS could also be referred to as central unit (CU),        eNB, gNB, or NodeB.    -   TRP: A transmission and reception point provides network        coverage and directly communicates with UEs. TRP could also be        referred to as distributed unit (DU) or network node.    -   Cell: A cell is composed of one or multiple associated TRPs,        i.e. coverage of the cell is composed of coverage of all        associated TRP(s). One cell is controlled by one BS. Cell could        also be referred to as TRP group (TRPG).

One or multiple of following assumptions for network side may be usedhereafter:

-   -   Downlink timing of TRPs in the same cell are synchronized.    -   RRC layer of network side is in BS.

One or multiple of following assumptions for UE side may be usedhereafter:

-   -   There are at least two UE (RRC) states: connected state (or        called active state) and non-connected state (or called inactive        state or idle state). Inactive state may be an additional state        or belong to connected state or non-connected state.

According to the RAN1 #95 agreement (as captured in the 3GPP RAN1 #95meeting report), two options for a Receiver UE (Rx) UE to transmit HARQfeedback to a Transmitter UE (Tx UE) in groupcast were introduced:

Option 1: A Receiver UE transmits HARQ-NACK on a PSFCH if it fails todecode a corresponding TB after decoding an associated PSCCH. Ittransmits no signal on the PSFCH otherwise.

Option 2: A Receiver UE transmits HARQ-ACK on a PSFCH if it successfullydecodes a corresponding TB. It transmits HARQ-NACK on a PSFCH if it doesnot successfully decode a corresponding TB after decoding an associatedPSCCH which targets the receiver UE.

Issue: Procedure(s) Regarding—a Receiver UE Obtaining Information forDetermining—Feedback Resource(s) (for the Receiver UE) for Groupcast isUnknown.

According to the RAN1 #97 meeting discussion, an implicit mechanism hasbeen introduced for a Rx UE to determine at least frequency and/or codedomain resource(s) of PSFCH in response to a PSSCH (Physical SidelinkShared Channel). The implicit mechanism comprises using an identifier todistinguish each Rx UE in a group for Option 2 groupcast HARQ feedbackmentioned above. In other words, a Rx UE could determine frequencyand/or code domain resource(s) at least based on an identifierassociated with the Rx UE. The value of the identifier associated withthe Rx UE is different with other Rx UEs in the group. The presentinvention discusses possible solutions for Rx UEs to determineidentifiers associated with sidelink feedback resource(s).

Solution 1: The UE could Determine Sidelink Feedback Resource(s) Basedon Information Provided by an Upper Layer (of the UE).

One general concept of the present invention is that a UE coulddetermine sidelink feedback resource(s) (by the UE itself) based oninformation provided by an upper layer (of the UE). The sidelinkfeedback resource(s) could be used to transmit sidelink HARQ feedbackassociated with or in response to at least one groupcast transmission.

In one embodiment, the UE could derive an identifier based on theinformation provided by the upper layer (of the UE). The identifiercould be associated with the sidelink feedback resource(s). Theidentifier could be associated with a PSFCH used to transmit sidelinkHARQ feedback associated with at least one groupcast transmission. Theidentifier could be associated with frequency and/or code domainresource(s) of a PSFCH. Additionally or alternatively, the identifiercould be associated with slot(s) of a PSFCH. Additionally oralternatively, the identifier could be associated with a (part of)PSFCH.

Additionally or alternatively, the UE could obtain the identifier fromthe upper layer (of the UE). The identifier could be contained in theinformation. The information provided by the upper layer could containgroup identifier information, Application-layer V2X Group identifier,source layer-2 ID, and/or destination layer-2 ID.

In one example, the UE could determine the value of the identifier atleast based on source layer-2 ID provided by the upper layer. The UEcould determine the value of the identifier at least based on one ormore digits of the source layer-2 ID. In another example, the UE coulddetermine the value of the identifier at least based on one or moredigits of the destination layer-2 ID. In an additional example, the UEcould determine the value of the identifier at least based on one ormore digits of the Application-layer V2X Group identifier.

An example is shown in FIG. 9. In particular, FIG. 9 shows UEsdetermining feedback resources for groupcast based on identifiers. Anupper layer of a first UE (UE 1) provides an identifier (member ID inthe group, id1) to (a lower layer of) the first UE, and an upper layerof a second UE (UE 2) provides an identifier (member ID in the group,id2) to (a lower layer of) the second UE. When a groupcast transmissionis received by the first and the second UE. The UEs (first UE and secondUE) could determine the frequency and/or code domain location offeedback resource(s) at least based on the identifiers provided by theirupper layer. Each identifier could map to one feedback resource. The UEwith identifier id1 could use feedback resource 1 for HARQ feedbacktransmission, and the UE with identifier id2 could use feedback resource2 for HARQ feedback transmission.

The groupcast transmission could be associated with feedback resourcesfor which each member in the group cannot be associated with onefeedback resource. In other words, number of the feedback resourcescould be less than number of UEs in the group. This alternative may notbe suitable for this situation. Alternatively, the groupcasttransmission could be associated with feedback resources for which atleast each member in the group can be associated with one feedbackresource.

An example is shown in FIG. 10. In particular, FIG. 10 shows UEs usingtheir identifier (source layer-2 ID) to determine sidelink feedbackresources. Three UEs (UE1, UE2, UE3) performs groupcast communication ina group. In response to receiving a groupcast transmission, each of theUEs determines feedback resource(s) associated with the groupcasttransmission at least based on slot, frequency information of thegroupcast transmission and its identifier (e.g. source Layer-2 ID,member ID in the group or etc.). The groupcast transmission isassociated with a total of 6 feedback resources (each feedback resourceassociated with each parameter a to f in FIG. 10). Additionally oralternatively, each feedback resource could be associated with an index(e.g. 0 to 5 in FIG. 10). Each of the UEs could determine which feedbackresource to use for transmitting HARQ feedback based on the remainder ofits identifier (e.g. source Layer-2 ID, member ID in the group or etc.)when divided by the number of the feedback resources. UE1 calculates theremainder of its source Layer-2 ID (i.e. remainder of 102 when dividedby 6) and use the feedback resource associated with an index of the samevalue as the remainder, which is feedback resource with index 0 in FIG.10.

In another example, a UE could determine its feedback resourceassociated with a groupcast transmission in a group at least based on anorder associated with identifiers (e.g. source layer-2 ID) of one ormore than one UEs in the group. In one embodiment, the UE could receivesource layer-2 ID(s) of other UEs in the group from its upper layer. TheUE could determine a feedback resource to transmit HARQ feedbackassociated with a groupcast transmission among one or more than onefeedback resource(s) (at a timing) based on a position of the value ofits identifier among values of identifiers of one or more than one UEsin the group. The identifiers of the UEs in the group could be sorted(in increasing order or in decreasing order), and each identifier of thesorted identifiers could be associated with one of the feedbackresources in sequence.

An illustration of the example is in FIG. 11. In particular, FIG. 11shows UEs determining feedback resources based on value of source ID(s).As shown in FIG. 11, there are three UEs performing groupcastcommunication (UE1, UE2, and UE3) in a group. The UEs knows itsidentifier (e.g. source layer-2 ID or member ID) and identifiers of(all) other UEs in the group. When receiving a groupcast transmission,the UEs associate six feedback resources (feedback resource from a to fin FIG. 11) with the groupcast transmission (e.g. the feedback resourcesare in a slot and/or frequency associated with the groupcasttransmission).

Additionally or alternatively, each of the feedback resources could beassociated with an index (e.g. feedback resource a could be associatedwith index 0). Each of the UEs determines which feedback resource amongthe six feedback resources to use at least based on the position of thevalue of its identifier comparing with identifiers of the other UEs inthe group. UE1 has an identifier with a 2^(nd) lowest value (i.e. 102)in the group, UE1 could determine to use the feedback resource with2^(nd) lowest frequency value among the feedback resources (e.g.feedback resource b).

Additionally or alternatively, UE1 could determine to use the feedbackresource associated with the 2^(nd) smallest index (e.g. the feedbackresource b). Additionally or alternatively UE2 has an identifier withsmallest value (i.e. 101) in the group, so UE2 determines to use thefeedback resource with the smallest index (the feedback resource withindex 0). Additionally or alternatively, UE2 could determine to use thefeedback resource with the lowest frequency value among the feedbackresources (e.g. feedback resource a). UE3 has an identifier with a3^(rd) lowest value (i.e. 107), so UE 3 determines to use the feedbackresource with the 3^(rd) smallest index (the feedback resource withindex 2). Additionally or alternatively, UE3 could determine to use thefeedback resource with the 3^(rd) lowest frequency value among thefeedback resources.

Additionally or alternatively, as illustrated in FIG. 12, UE3 couldselect a feedback resource associated with the highest index (i.e. index5) or the feedback resource with highest frequency value among thefeedback resources since UE3 has the highest value of identifier amongall the UEs in the group. Additionally or alternatively, UE2 couldselect a feedback resource associated with the 2^(nd) highest index(i.e. index 4) or the feedback resource with 2^(nd) highest frequencyvalue among the feedback resources since UE2 has the 2^(nd) highestvalue of identifier among all the UEs in the group. Additionally oralternatively, UE1 could select a feedback resource associated with the3^(rd) highest index (i.e. index 3) or the feedback resource with 3^(rd)highest frequency value among the feedback resources since UE1 has the3^(rd) highest value of identifier among all the UEs in the group.

In another example, information provided by the upper layer couldinclude frequency and/or code domain resource(s) of a PSFCH, and the UEcould use the frequency and/or code domain resource(s) for transmittingHARQ feedback associated with or in response to a groupcasttransmission.

Solution 2: A Leader UE of a Group Provides Information aboutAssociation Between Sidelink Feedback Resource(s) and UE(s) to theGroup.

The general concept is that a leader UE in a group (or a platoon) of UEscould provide information associated with sidelink feedback resource(s)to one or more UEs in the group. The one or more UEs in the group coulddetermine sidelink feedback resource(s) associated with groupcasttransmission transmitted from other UEs in the group at least based onthe information provided by the leader UE. Additionally oralternatively, the one or more UEs in the group could determine sidelinkfeedback resource(s) associated with groupcast transmission transmittedfrom other UEs in the group at least based on an identifier (e.g.,source layer-2 ID, member ID in the group or etc.) associated with theone or more UEs.

The information could contain a list of the association between sidelinkfeedback resource(s) and UE(s). Each entry of the list could contain anidentifier of a UE and an identifier used to identify a sidelinkfeedback resource for the UE.

The information could contain a first identifier group associated withthe one or more UEs. In one embodiment, each of the one or more UEscould be associated with an identifier in the first identifiers group.Each identifier in the first group may have a value different from thevalues of the other identifiers in the first identifier group.

The information could contain a second identifier group associated withthe one or more UEs. The one or more UEs could determine sidelinkfeedback resource(s) associated with groupcast communications at leastbased on the second group of identifiers.

The information could contain a mapping between the identifiers in thefirst group and the identifiers in the second group. Additionally oralternatively, the information could contain a mapping between each ofthe one or more UEs and one or more sidelink feedback resource(s)associated with groupcast communications.

The information could contain information associated with the leader UE(e.g. mapping between UE and sidelink feedback resource or identifier(s)of the leader UE). Additionally or alternatively, the information maynot contain information associated with the leader UE. As an example, amessage transmitted by a leader UE in a group may contain informationassociated with one or more feedback resources. The one or more feedbackresources could be associated with one or more groupcast transmissions,one or more transmitter UEs, and/or one or more receiver UEs.

The information could contain a mapping between the one or more receiverUEs and the one or more feedback resources. Additionally oralternatively, the information could contain a mapping between the oneor more transmitter UEs and the one or more feedback resources.

FIG. 13 shows an exemplary message in accordance with one embodiment. Asshown in FIG. 13, each identifier in a first identifier group could beassociated with a UE in the group (e.g., UEID_1 is associated with UE1,UEID_2 is associated with UE2, and UEID_3 is associated with UE3). Eachidentifier in a second identifier group could be associated with afeedback resource of the one or more feedback resources (e.g.identifier_1, identifier_2, and identifier_3 are associated withdifferent feedback resources in the one or more feedback resources). Inthe example, UE1 could determine a feedback resource to transmit HARQfeedback to a transmitter UE in response to a groupcast transmissiontransmitted by the transmitter UE at least based on identifier_1 in theinformation. The transmitter UE could be the leader UE, UE2, or UE3.Preferably, UE1 uses a same identifier in the second identifier group(e.g., identifier_1) for all transmitter UEs to determine feedbackresources to transmit HARQ feedbacks in in response to groupcasttransmissions from the all transmitter UEs.

Additionally or alternatively, as shown in FIG. 14A and FIG. 14B, themessage transmitted by the leader UE in the group contains informationassociated with one or more feedback resources. The message contains amapping between transmitter UEs and identifiers associated with feedbackresources for each receiver UE in the group. A receiver UE coulddetermine a feedback resource for transmitting a HARQ feedback to atransmitter UE in response to a groupcast transmission from thetransmitter UE at least based on the transmitter UE and the mapping forthe receiver UE.

In an example associated with FIG. 14A, when the (RX) UE1 receives agroupcast transmission from the (TX) UE2, the (RX) UE1 uses Identifier1to determine a feedback resource from the one or more feedback resourcesto transmit a HARQ feedback to the (TX) UE2. Additionally oralternatively, when the (RX) UE1 receives a groupcast transmission fromthe (TX) UE3, the (RX) UE1 uses Identifier2 to determine a feedbackresource from the one or more feedback resources to transmit a HARQfeedback to the (TX) UE3.

In another example associated with FIG. 14B, when the (RX) UE1 receivesa groupcast transmission from the (TX) UE2, the (RX) UE1 usesIdentifier3 to determine a feedback resource from the one or morefeedback resources to transmit a HARQ feedback to the (TX) UE2.Additionally or alternatively, when the (RX) UE1 receives a groupcasttransmission from the (TX) UE3, the (RX) UE1 uses Identifier5 todetermine a feedback resource from the one or more feedback resources totransmit a HARQ feedback to the (TX) UE3.

Additionally or alternatively, the leader UE could use one or morespecific feedback resources to transmit HARQ feedback in response togroupcast transmission for all transmitter UEs. Additionally oralternatively, the leader UE could use a fixed feedback resource totransmit HARQ feedback in response to receiving a groupcasttransmission.

The message could be transmitted by the leader UE via groupcasttransmission and/or via broadcast transmission. Each identifier in thefirst identifier group could be source-layer2 ID of the UE associatedwith each identifier. Each identifier in the second identifier groupcould be an index associated with a feedback resource in the one or morefeedback resources.

Solution 3: A Transmitter UE of a Group Provides Information aboutAssociation Between Sidelink Feedback Resource(s) and Receiver UE(s) tothe Group.

The general concept is that a transmitter UE in a group could provideinformation associated with sidelink feedback resource(s) to one or more(receiver) UEs. The information could contain a list of the associationbetween sidelink feedback resource(s) and receiver UE(s). Each entry ofthe list could contain an identifier of a receiver UE and an identifierused to identify a sidelink feedback resource for the receiver UE. Thereceiver UE is in view of the transmitter UE sending this information.

The one or more UEs could determine sidelink feedback resource(s)associated with groupcast transmissions transmitted by the transmitterUE at least based on the information provided by the transmitter UE. Theone or more UEs may not determine sidelink feedback resource(s)associated with groupcast transmissions transmitted by the transmitterUE based on the information provided by other transmitter UEs.Additionally or alternatively, the one or more UEs could determinesidelink feedback resource(s) associated with groupcast transmission(transmitted by the transmitter UE) at least based on one or moreidentifiers associated with one or more UEs in the group provided by anupper layer and the information provided by the transmitter UE.

In an example shown in FIG. 15, there are 3 UEs (i.e. UE1, UE2, and UE3)in a group for groupcast communication. UE1 could transmit a firstmessage (e.g. UE1 Message) associated with sidelink feedback resourcesto UE2 and UE3. UE1 could perform a groupcast transmission to transmitthe first message to one or more UEs. The first message could indicate asource layer-2 ID or a member ID associated with UE1. Additionally oralternatively, UE2 could transmit a second message (e.g. UE2 Message)associated with sidelink feedback resources to UE1 and UE3. UE2 couldperform a groupcast transmission to transmit the second message to oneor more UEs in the group. The second message could indicate a sourcelayer-2 ID or a member ID associated with UE2. Additionally oralternatively, UE3 could transmit a third message (e.g. UE3 Message)associated with sidelink feedback resources to UE1 and UE2. UE3 couldperform a groupcast transmission to transmit the third message to one ormore UEs in the group. The third message could indicate a source layer-2ID or a member ID associated with UE3.

The first message could contain identifiers associated with UE2 and UE3(e.g. UEID_2 and UEID_3). The identifiers associated with UE2/UE3 couldbe source layer-2 ID or member ID of UE2/UE3. The first message couldcontain identifiers associated with feedback resources (e.g.identifier_1 and identifier_2). The first message could contain amapping between UE2/UE3 and sidelink feedback resource(s). Whenreceiving a groupcast transmission transmitted from UE1, UE2 and UE3could determine sidelink feedback resource(s) in response to thegroupcast transmission based on identifiers_1 and identifier_2,respectively.

The second message could contain identifiers associated with UE1 and UE3(e.g. UEID_1 and UEID_3). The identifiers associated with UE1/UE3 couldbe source layer-2 ID or member ID of UE1/UE3. The second message couldcontain identifiers associated with feedback resources (e.g.identifier_3 and identifier_4). The second message could contain amapping between UE1/UE3 and sidelink feedback resource(s). Whenreceiving a groupcast transmission transmitted from UE2, UE1 and UE3could determine sidelink feedback resource(s) in response to thegroupcast transmission based on identifiers_3 and identifier_4,respectively.

The third message could contain identifiers associated with UE1 and UE2(e.g. UEID_1 and UEID_2). The identifiers associated with UE1/UE2 couldbe source layer-2 ID or member ID of UE1/UE2. The third message couldcontain identifiers associated with feedback resources (e.g.identifier_5 and identifier_6). The third message could contain amapping between UE1/UE2 and sidelink feedback resource(s). Whenreceiving a groupcast transmission transmitted from UE3, UE1 and UE2could determine sidelink feedback resource(s) based on identifier_5 andidentifier_6, respectively.

An example is shown in FIG. 16. A Tx UE performs groupcast communicationwith 3 Rx UEs (Rx UE1, Rx UE2, and Rx UE3) in a group. Each of the 3 RxUEs receives (or obtains) a member ID from an upper layer of the Rx UE(e.g. member ID_1 for Rx UE1, member ID_2 for Rx UE2 and member ID_3 forRx UE3). The member ID could be associated with the group. The value ofeach member ID is different from other member IDs of other Rx UEs in thegroup (e.g. the member IDs are used to distinguish Rx UEs in the group).The Rx UE is associated with a ID (Src ID). The ID could be (Layer-1 orLayer-2) source ID of the Tx UE. The ID or part of the ID could beprovided by the Tx UE to the Rx UEs (e.g. via groupcast transmissions).The Tx UE could perform groupcast transmission to transmit sidelink datato the 3 Rx UEs. The groupcast transmission may be associated with 6feedback resources. Each feedback resource is associated with an index.The Rx UEs could determine feedback resource associated with thegroupcast transmission at least based on (each) member ID and the ID(Src ID) associated with the Tx UE. For example, the Rx UEs maydetermine an index among the indexes of the feedback resources (e.g. 0to 5) based on the (each) member ID and the Src ID. For example, Rx UE1could determine or derive index number 1 based on member ID_1 and SrcID. The Rx UE1 could then transmit feedback to Tx UE via feedbackresource associated with index 1.

The first, second, and/or third message could be a (PC5) RRC message ora MAC control element. The information could be transmitted to thesecond UE via a (PC5) RRC signaling and/or via unicast message. Theinformation could be transmitted via groupcast and/or broadcast. Theinformation could contain source Layer-2 ID of the Tx UE. Theinformation could be indicative of one or more digits/bits or part ofthe source Layer-2 ID of the Tx UE.

For all concepts, solutions and examples above:

-   -   The upper layer could be a V2X application layer, a V2X layer, a        NAS layer of the UE, and/or a protocol stack above physical        layer.    -   The upper layer could be above the AS layer.    -   The sidelink feedback resource(s) could be a PSFCH or a PSSCH.    -   The sidelink feedback resource(s) could be frequency and/or code        domain resource(s) associated with the identifier.    -   The identifier could be the source layer-2 ID of a UE or the        destination layer-2 ID of a UE.    -   The identifier could be group identifier information or        Application-layer V2X Group identifier.    -   The group could comprise one or more than one UEs for groupcast        communication, or one or more transmitter UEs (Tx UEs) for        groupcast transmission.    -   The transmitter UEs could perform a groupcast transmissions in a        group.    -   The information associated with sidelink feedback resource(s)        could be a MAC CE or a (PC5) RRC message.    -   The information associated with sidelink feedback resource(s)        could be used to configure feedback resource(s) for one or more        UEs in a group for groupcast communication.    -   The leader UE may not have RRC unicast connection with the        receiver UE(s).    -   The transmitter UE may not have RRC unicast connection with the        receiver UE(s).

FIG. 17 is a flow chart 1700 according to one exemplary embodiment fromthe perspective of a first device for determining sidelink feedbackresource associated with sidelink communication. In step 1705, the firstdevice receives an identifier from an upper layer of the first device.In step 1710, the first device receives a sidelink transmission from asecond device. In step 1715, the first device determines a sidelinkfeedback resource associated with the sidelink transmission at leastbased on the identifier and a source ID associated with the sidelinktransmission. In step 1720, the first device uses the sidelink feedbackresource to transmit a feedback in response to the sidelink transmissionto the second device.

In one embodiment, the first device could determine the sidelinkfeedback resource further based on the remainder of the identifierdivided by a (total) number of sidelink feedback resources associatedwith the sidelink transmission. The sidelink feedback resource could beassociated with an index, and/or the index associated with the sidelinkfeedback resource could be equal to and/or associated with the remainderof the identifier divided by a (total) number of sidelink feedbackresources associated with the sidelink transmission.

In one embodiment, the upper layer could be V2X application layer of thefirst device or V2X layer of the first device. The identifier could bemember ID of the first device associated with a group, wherein the firstdevice performs the sidelink communication for the group. Each device inthe group could be associated with a member ID different from member IDsassociated with other devices in the group.

In one embodiment, the source ID could be a part of layer-2 source ID ofthe second device. The sidelink transmission could be groupcasttransmission.

In one embodiment, the first device transmits the feedback as HARQ-ACKon the sidelink feedback resource if the first device successfullydecodes the sidelink transmission, and/or the first device transmits thefeedback as HARQ-NACK on the sidelink feedback resource if the firstdevice does not successfully decode the sidelink transmission.

Referring back to FIGS. 3 and 4, in one exemplary embodiment of a firstdevice for determining sidelink feedback resource associated withsidelink communication. The first device 300 includes a program code 312stored in the memory 310. The CPU 308 could execute program code 312 toenable the first device (i) to receive an identifier from an upper layerof the first device, (ii) to receive a sidelink transmission from asecond device, (iii) to determine a sidelink feedback resourceassociated with the sidelink transmission at least based on theidentifier and a source ID associated with the sidelink transmission,and (iv) to use the sidelink feedback resource to transmit a feedback inresponse to the sidelink transmission to the second device. Furthermore,the CPU 308 can execute the program code 312 to perform all of theabove-described actions and steps or others described herein.

FIG. 18 is a flow chart 1800 according to one exemplary embodiment fromthe perspective of a second device for receiving sidelink feedback(s)associated with sidelink communication. In step 1805, the second devicetransmits a sidelink transmission to at least a first device in a group.In step 1810, the second device receives, on a sidelink feedbackresource, a feedback in response to the sidelink transmission from thefirst device, wherein the sidelink feedback resource is determined atleast based on an identifier of the first device and a source IDassociated with the sidelink transmission.

In one embodiment, the sidelink feedback resource could be determinedbased on the remainder of the identifier divided by a (total) number ofsidelink feedback resources associated with the sidelink transmission.The sidelink feedback resource could be associated with an index, and/orthe index associated with the sidelink feedback resource could be equalto and/or associated with the remainder of the identifier divided by a(total) number of sidelink feedback resources associated with thesidelink transmission.

In one embodiment, the identifier of the first device could be receivedfrom an upper layer of the first device, and/or the upper layer is V2Xapplication layer of the first device or V2X layer of the first device.The identifier could be member ID (Identity) of the first deviceassociated with the group. Each device in the group could be associatedwith a member ID (Identity) different from member IDs associated withother devices in the group.

In one embodiment, the second device could transmit the sidelinktransmission to a plurality of devices in a group. Furthermore, thesecond device could receive, on a plurality of sidelink feedbackresources, a plurality of feedbacks associated with the sidelinktransmission from the plurality of devices in the group, wherein each ofthe plurality of sidelink feedback resources is determined at leastbased on an identifier of one corresponding device among the pluralityof devices and the source ID associated with the sidelink transmission.The identifier of the one corresponding device could be member ID of theone corresponding device associated with the group.

In one embodiment, the source ID could be a part of layer-2 source ID ofthe second device. The sidelink transmission could be groupcasttransmission.

In one embodiment, if the second device could receive the feedback asHARQ-ACK on the sidelink feedback resource, the second device considersthe sidelink transmission is successfully decoded by the first device.Furthermore, if the second device receives the feedback as HARQ-NACK onthe sidelink feedback resource, the second device could consider thesidelink transmission is not successfully decoded by the first device.

Referring back to FIGS. 3 and 4, in one exemplary embodiment of a seconddevice for receiving sidelink feedback(s) associated with sidelinkcommunication. The second device 300 includes a program code 312 storedin the memory 310. The CPU 308 could execute program code 312 to enablethe second device (i) to transmit a sidelink transmission to at least afirst device in a group, and (ii) to receive, on a sidelink feedbackresource, a feedback in response to the sidelink transmission from thefirst device, wherein the sidelink feedback resource is determined atleast based on an identifier of the first device and a source IDassociated with the sidelink transmission. Furthermore, the CPU 308 canexecute the program code 312 to perform all of the above-describedactions and steps or others described herein.

FIG. 19 is a flow chart 1900 according to one exemplary embodiment fromthe perspective of a first device for determining HARQ feedbackresource(s) associated with a groupcast transmission. In step 1905, thefirst device receives information from an upper layer of the firstdevice. In step 1910, the first device determines an identifier based onthe information from the upper layer. In step 1915, the first devicereceives a groupcast transmission from a second device. In step 1920,the first device determines HARQ feedback resource(s) associated withthe groupcast transmission at least based on the identifier. In step1925, the first device uses the HARQ feedback resource(s) to transmit asidelink HARQ feedback to the second device.

Referring back to FIGS. 3 and 4, in one exemplary embodiment of a firstdevice for determining HARQ feedback resource(s) associated with agroupcast transmission. The first device 300 includes a program code 312stored in the memory 310. The CPU 308 could execute program code 312 toenable the first device (i) to receive information from an upper layerof the first device, (ii) to determine an identifier based on theinformation from the upper layer, (iii) to receive a groupcasttransmission from a second device, (iv) to determine HARQ feedbackresource(s) associated with the groupcast transmission at least based onthe identifier, and (v) to use the HARQ feedback resource(s) to transmita sidelink HARQ feedback to the second device. Furthermore, the CPU 308can execute the program code 312 to perform all of the above-describedactions and steps or others described herein.

FIG. 20 is a flow chart 2000 according to one exemplary embodiment fromthe perspective of a first device for determining HARQ feedbackresource(s) associated with a groupcast transmission. In step 2005, thefirst device receives an information from a second device. In step 2010,the first device derives one or more identifiers based on theinformation. In step 2015, the first device receives a groupcasttransmission from a third device. In step 2020, the first devicedetermines HARQ feedback resource(s) associated with the groupcasttransmission at least based on the one or more identifiers. In step2025, the first device transmits a sidelink HARQ feedback to the thirddevice using the HARQ feedback resource(s).

Referring back to FIGS. 3 and 4, in one exemplary embodiment of a firstdevice for determining HARQ feedback resource(s) associated with agroupcast transmission. The first device 300 includes a program code 312stored in the memory 310. The CPU 308 could execute program code 312 toenable the first device (i) to receive an information from a seconddevice, (ii) to derive one or more identifiers based on the information,(iii) to receive a groupcast transmission from a third device, (iv) todetermine HARQ feedback resource(s) associated with the groupcasttransmission at least based on the one or more identifiers, and (v) totransmit a sidelink HARQ feedback to the third device using the HARQfeedback resource(s). Furthermore, the CPU 308 can execute the programcode 312 to perform all of the above-described actions and steps orothers described herein.

FIG. 21 is a flow chart 2100 according to one exemplary embodiment fromthe perspective of a first device for determining HARQ feedbackresource(s) associated with a groupcast transmission. In step 2105, thefirst device receives an information from a second device. In step 2110,the first device derives one or more identifiers based on theinformation. In step 2115, the first device receives a groupcasttransmission from the second device. In step 2120, the first devicedetermines HARQ feedback resource(s) associated with the groupcasttransmission at least based on the one or more identifiers. In step2125, the first device transmits a sidelink HARQ feedback to the seconddevice using the HARQ feedback resource(s).

Referring back to FIGS. 3 and 4, in one exemplary embodiment of a firstdevice for determining HARQ feedback resource(s) associated with agroupcast transmission. The first device 300 includes a program code 312stored in the memory 310. The CPU 308 could execute program code 312 toenable the first device (i) to receive an information from a seconddevice, (ii) to derive one or more identifiers based on the information,(iii) to receive a groupcast transmission from the second device, (iv)to determine HARQ feedback resource(s) associated with the groupcasttransmission at least based on the one or more identifiers, and (v) totransmit a sidelink HARQ feedback to the second device using the HARQfeedback resource(s). Furthermore, the CPU 308 can execute the programcode 312 to perform all of the above-described actions and steps orothers described herein.

In the context of embodiments illustrated in FIGS. 19-21 and discussedabove, in one embodiment, the first device could receive a TB via thegroupcast transmission, wherein the first device determines the HARQfeedback resource(s) further based on a source ID field of the TB(Transport Block). The first device could determine the HARQ feedbackresource(s) further based on a source layer-2 ID associated with thefirst device, the second device, or the third device. The first devicecould also determine the HARQ feedback resource(s) further based on atiming associated with the receiving of the groupcast transmission. Thefirst device could determine the HARQ feedback resource(s) further basedon a frequency (range) associated with the receiving of the groupcasttransmission.

In one embodiment, the first device could be a receiver UE (in a group).The second device could be the third device. Alternatively, the seconddevice may not be the third device.

In one embodiment, the second device may be a leader UE (in a group).Alternatively, the second device may not be the leader UE (in a group).The third device could be a transmitter UE (in a group).

In one embodiment, the information could indicate a mapping between oneor more devices and HARQ feedback resource(s). The information couldalso indicate a mapping between one or more devices and one or moreidentifiers associated with HARQ feedback resource(s). The informationmay not indicate a mapping between a leader UE (in a group) and HARQfeedback resource(s).

In one embodiment, the first device could transmit the sidelink HARQfeedback on a default HARQ feedback resource if the first device cannotdetermine the sidelink HARQ feedback resource based on the one or moreidentifiers.

FIG. 22 is a flow chart 2200 according to one exemplary embodiment fromthe perspective of a first device for configuring HARQ feedbackresource(s) for one or more devices associated with a groupcasttransmission. In step 2205, the first device transmits an information tothe one or more devices, wherein the information indicates a mappingbetween one or more sidelink feedback resource(s) to the one or moredevice(s). In step 2210, the first device performs a groupcasttransmission to the one or more devices. In step 2215, the first devicereceives one or more HARQ feedback from the one or more devices, whereineach of the one or more HARQ feedback from each of the one or moredevices is received on the sidelink feedback resource(s) mapped to theeach of the one or more devices.

In one embodiment, the information could indicate a mapping between theone or more sidelink feedback resource(s) and one or more identifiers,wherein each of the one or more identifiers may be associated with eachof the one or more device(s). In one embodiment, the information couldindicate a mapping between one or more identifiers and the one or moredevice(s), wherein each of the one or more identifiers may be associatedwith each of the one or more sidelink feedback resource(s). Theinformation could be transmitted via a RRC (Radio Resource Control)signaling, via broadcast, or via groupcast.

In one embodiment, the information could be a RRC message, a MAC (MediumAccess Control) CE (Control Element), or a TB (Transport Block). Theinformation may contain source layer-2 ID (of the first, second, orthird device), or destination layer-2 ID (of the first, second, or thirddevice). The information may also contain group identifier informationor Application-layer V2X Group identifier.

In one embodiment, the upper layer could be a V2X layer, a V2Xapplication layer, or a layer or protocol stack above MAC, RRC, and ASlayer.

Referring back to FIGS. 3 and 4, in one exemplary embodiment of a firstdevice for configuring HARQ feedback resource(s) for one or more devicesassociated with a groupcast transmission. The first device 300 includesa program code 312 stored in the memory 310. The CPU 308 could executeprogram code 312 to enable the first device (i) to transmit aninformation to the one or more devices, wherein the informationindicates a mapping between one or more sidelink feedback resource(s) tothe one or more device(s), (ii) to perform a groupcast transmission tothe one or more devices, and (iii) to receive one or more HARQ feedbackfrom the one or more devices, wherein each of the one or more HARQfeedback from each of the one or more devices is received on thesidelink feedback resource(s) mapped to the each of the one or moredevices. Furthermore, the CPU 308 can execute the program code 312 toperform all of the above-described actions and steps or others describedherein.

Various aspects of the disclosure have been described above. It shouldbe apparent that the teachings herein could be embodied in a widevariety of forms and that any specific structure, function, or bothbeing disclosed herein is merely representative. Based on the teachingsherein one skilled in the art should appreciate that an aspect disclosedherein could be implemented independently of any other aspects and thattwo or more of these aspects could be combined in various ways. Forexample, an apparatus could be implemented or a method could bepracticed using any number of the aspects set forth herein. In addition,such an apparatus could be implemented or such a method could bepracticed using other structure, functionality, or structure andfunctionality in addition to or other than one or more of the aspectsset forth herein. As an example of some of the above concepts, in someaspects concurrent channels could be established based on pulserepetition frequencies. In some aspects concurrent channels could beestablished based on pulse position or offsets. In some aspectsconcurrent channels could be established based on time hoppingsequences. In some aspects concurrent channels could be establishedbased on pulse repetition frequencies, pulse positions or offsets, andtime hopping sequences.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, processors, means, circuits, and algorithmsteps described in connection with the aspects disclosed herein may beimplemented as electronic hardware (e.g., a digital implementation, ananalog implementation, or a combination of the two, which may bedesigned using source coding or some other technique), various forms ofprogram or design code incorporating instructions (which may be referredto herein, for convenience, as “software” or a “software module”), orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentdisclosure.

In addition, the various illustrative logical blocks, modules, andcircuits described in connection with the aspects disclosed herein maybe implemented within or performed by an integrated circuit (“IC”), anaccess terminal, or an access point. The IC may comprise a generalpurpose processor, a digital signal processor (DSP), an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) or other programmable logic device, discrete gate or transistorlogic, discrete hardware components, electrical components, opticalcomponents, mechanical components, or any combination thereof designedto perform the functions described herein, and may execute codes orinstructions that reside within the IC, outside of the IC, or both. Ageneral purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

It is understood that any specific order or hierarchy of steps in anydisclosed process is an example of a sample approach. Based upon designpreferences, it is understood that the specific order or hierarchy ofsteps in the processes may be rearranged while remaining within thescope of the present disclosure. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

The steps of a method or algorithm described in connection with theaspects disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module (e.g., including executable instructions and relateddata) and other data may reside in a data memory such as RAM memory,flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a harddisk, a removable disk, a CD-ROM, or any other form of computer-readablestorage medium known in the art. A sample storage medium may be coupledto a machine such as, for example, a computer/processor (which may bereferred to herein, for convenience, as a “processor”) such theprocessor can read information (e.g., code) from and write informationto the storage medium. A sample storage medium may be integral to theprocessor. The processor and the storage medium may reside in an ASIC.The ASIC may reside in user equipment. In the alternative, the processorand the storage medium may reside as discrete components in userequipment. Moreover, in some aspects any suitable computer-programproduct may comprise a computer-readable medium comprising codesrelating to one or more of the aspects of the disclosure. In someaspects a computer program product may comprise packaging materials.

While the invention has been described in connection with variousaspects, it will be understood that the invention is capable of furthermodifications. This application is intended to cover any variations,uses or adaptation of the invention following, in general, theprinciples of the invention, and including such departures from thepresent disclosure as come within the known and customary practicewithin the art to which the invention pertains.

What is claimed is:
 1. A method for a first device to determine sidelinkfeedback resource associated with sidelink communication, comprising:receiving an identifier from an upper layer of the first device;receiving a sidelink transmission from a second device; determining asidelink feedback resource associated with the sidelink transmission atleast based on the identifier and a source Identity (ID) associated withthe sidelink transmission and further based on a remainder of theidentifier divided by a total number of sidelink feedback resourcesassociated with the sidelink transmission; and using the sidelinkfeedback resource to transmit a feedback in response to the sidelinktransmission to the second device.
 2. The method of claim 1, wherein thesidelink feedback resource is associated with an index.
 3. The method ofclaim 1, wherein the upper layer is Vehicle-to-Everything (V2X)application layer of the first device or V2X layer of the first device.4. The method of claim 1, wherein the identifier is member ID of thefirst device associated with a group.
 5. The method of claim 4, whereinthe first device performs the sidelink communication for the group. 6.The method of claim 4, wherein each device in the group is associatedwith a member ID different from member IDs associated with other devicesin the group.
 7. The method of claim 1, wherein the source ID is a partof layer-2 source ID of the second device.
 8. The method of claim 1,wherein the sidelink transmission is groupcast transmission.
 9. Themethod of claim 1, wherein the first device transmits the feedback asHybrid Automatic Repeat Request-Acknowledgement (HARQ-ACK) on thesidelink feedback resource if the first device successfully decodes thesidelink transmission.
 10. The method of claim 1, wherein the firstdevice transmits the feedback as Hybrid Automatic RepeatRequest-Negative Acknowledgement (HARQ-NACK) on the sidelink feedbackresource if the first device does not successfully decode the sidelinktransmission.
 11. A method for a second device to receive sidelinkfeedback associated with sidelink communication, comprising:transmitting a sidelink transmission to at least a first device in agroup; and receiving, on a sidelink feedback resource, a feedbackassociated with the sidelink transmission from the first device, whereinthe sidelink feedback resource is determined at least based on anidentifier of the first device and a source Identity (ID) associatedwith the sidelink transmission and further based on a remainder of theidentifier divided by a total number of sidelink feedback resourcesassociated with the sidelink transmission.
 12. The method of claim 11,wherein the sidelink feedback resource is associated with an index. 13.The method of claim 11, wherein the identifier of the first device isreceived from an upper layer of the first device, and/or the upper layeris Vehicle-to-Everything (V2X) application layer of the first device orV2X layer of the first device.
 14. The method of claim 11, wherein theidentifier is member ID of the first device associated with the group.15. The method of claim 14, wherein each device in the group isassociated with a member ID different from member IDs associated withother devices in the group.
 16. The method of claim 11, furthercomprising: the second device transmits the sidelink transmission to aplurality of devices in a group; and the second device receives, on aplurality of sidelink feedback resources, a plurality of feedbacksassociated with the sidelink transmission from the plurality of devicesin the group, wherein each of the plurality of sidelink feedbackresources is determined at least based on an identifier of onecorresponding device among the plurality of devices and the source IDassociated with the sidelink transmission.
 17. The method of claim 16,wherein the identifier of the one corresponding device is member ID ofthe one corresponding device associated with the group.
 18. The methodof claim 11, wherein the source ID is a part of layer-2 source ID of thesecond device.
 19. The method of claim 11, wherein the sidelinktransmission is groupcast transmission.
 20. The method of claim 11,wherein if the sidelink transmission receives the feedback as HybridAutomatic Repeat Request-Acknowledgement (HARQ-ACK) on the sidelinkfeedback resource, the second device considers the sidelink transmissionsuccessfully decoded by the first device, and/or if the second devicesreceives the feedback as Hybrid Automatic Repeat Request-NegativeAcknowledgement (HARQ-NACK) on the sidelink feedback resource, thesecond device considers the sidelink transmission not successfullydecoded by the first device.